THE  ANALYSIS  OF  PARIS  GREEN 


BY 

EDITH  FIELD  CLOYES 


THESIS 

FOR  THE 

degree  OF  BACHELOR  OF  SCIENCE 

IN 

LIBERAL  ARTS  AND  SCIENCES 


COLLEGE  OF  LIBERAL  ARTS  AND  SCIENCES 


UNIVERSITY  OF  ILLINOIS 


1922 


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Digitized  by  the  Internet  Archive 
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https://archive.org/details/analysisofparisgOOcloy 


Table  of  Contents. 

I .  Acknowledgement • 

II.  Historical. 

III.  Description  of  method  used. 

IV.  Part  II.  The  Ratio  of  Potassium  Iodide  to  Copper  in 

the  lodometric  Method. 

V • Experimental . 

VI.  Conclusions. 

VII.  Bibliography. 


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The  writer  wishes  to  express  her  appreciation  for  the 
inspiration  and  helpful  suggestions  received  from  Dr.G*D* 
Beal^  under  whose  supervision  this  work  has  heen  carried 
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— 

Historical, 

During  the  last  decade,  work  on  the  analysis  of  Paris  Green 
and  similar  insecticides  and  fungicides  has  been  pursued  with 
greater  diligence,  due  in  part  to  the  inrestigations  stimujr 
lated  by  the  AssocAation  of  Official  Agricultural  Chemists* 

The  Sureau  at  Washington  sent  out  calls  for  work  on  this  com- 
pound to  many  experiment  stations,  with  the  result  that  serera; 
methods  for  its  analysis,  or  for  the  ascertaining  of  both  the 
copper  and  arsenic  content  thereof,  were  brought  forward*  The 
following  are  some  of  the  most  important  of  them: 

j. 

Hedges’  Method  for  Arsenious  Oxide  in  Paris  Green.  This 
method  calls  for  a 2 gram  sample  which  is  dissolved  in  50  cubic 
centimeters  of  (1:1)  hydrochloric  acid,  at  a temperature  not 
to  exceed  80° Centigrade,  when  dissolved;  the  solution  is  made 
up  to  250  cubic  centimeters  with  watery  then  25  cubic  centi- 
meters of  this  are  taken,  and  made  up  to  a volume  of  300  cubic 
centimeters,  when  an  excess  of  sodium  bicarbonate  is  added, 
and  the  solution  titrated  with  twentieth  normal  Iodine  solutioi  , 
C.M. Smith  Method  for  Arsenious  Oxide  in  Paris  Green. A 2 grar 
sample  is  treated  with  50  cubic  centimeters  each  of  water  and 
(1:4)  sulphuric  acid;  after  solution^ water  is  added  to  make 
250  cubic  centimeters  of  the  solution;  then  25  centimeters  of 
this  are  taken  and  diluted  to  150-200  cubic  centimeters,  when 
it  is  neutralized  with  sodium  bicarbonate,  10  grams  in  excess 
added,  also  5 grams  of  ammonium  chloride,  and  then  it  As  tit- 
rated with  twentieth  normal  Iodine  solution* 

Various  comments  for  and  against  these  methods  have  been 
made  by  different  analysts,  for  example, - 

E.R.Tobey:”!  much  prefer  Hedges*  Method  to  the  C.M. Smith  or 


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2 


eren  the  official  methods*” 

S*D.ATeritt Results  show  one  method  as  good  as  the  other. 
Leare  it  to  the  choice  of  the  worker.” 

0. B.\?inter : ” smith  and  Hedges*  methods  are  quicker  than  the 
official  method,  hut  they  rim  slightly  lower.” 

J.J.T. Graham  and  F.L. Elliot  prefer  the  Smith  method  to  that 
og  Hedges  as  there  is  no  danger  of  losing  any  arsenic  when 
Paris  Green  is  dissolved  in  sulphuric  acid;  whereas  when  hydro 
chloric  acid  is  used,  the  temperature  must  he  watched  oarefull 
or  the  arsenious  chldride  is  lost.  The  results  do  not  check  as 
well  as  might  he  expected,  hut  this  is  due  in  part  to  ©rrors 
in  standardization  of  the  Iodine  solution.  The  results  with 
Hedges*  method  run  slightly  lower  than  those  of  the  official 
method,  hut  it  was  found  that  if  the  temperature  was  lowered 
the  results  were  better.  Smith *s  method  also  gave  lower  result 

Both  methods  are  easy,  quick,  and  accurate  for  determining  the 

arser.iou^:  oxide,  hut  not  applicahle  for  deterraining  the 

total  arsenic  where  a part  is  in  the  form  of  the  arsenate. 

The  use  of  sulphuric  acid  instead  of  hydrochloric  acid  in 
the  official  method  has  the  following  advantages: 

1.  There  is  no  danger  of  losing  arsenic  as  arsenic  tri- 
chloride. The  reduction  of  the  arsenic  oxide  to  assenious 
oxide  is  always  complete, and  better  agreeing  results  are 
given,  with  less  care  in  manipulation. 

2. 

Less  acid  and  potassium  iodide  are  needed  here,  so  that 
it  is  a cheaper  method,  and  less  time  is  required  for 
neutralization. 

The  method  of  determining  arsenic  by  distillation  with  hydro- 
chloric acid  is  very  accurate.  The  Referee,  R.C. Roark,  recom- 


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mended  that  these  methods  he  adopted  as  official,  and  that  the 
present  official  methods  he  discarded. 

R.C .Roark  regards  the  distillation  method  as  hy  far  the 
most  accurate.  Several  distillations  can  he  made  at  the  same 
time.  The  distillate  can  he  kept  any  length  of  time.  The  arsen- 
ic can  he  determined  in  hoth  forms  and  separate  from  antimony. 
He  says  the  Hedges*  and  Smith  methods  are  quick  and  useful  for 
approximate  analysis,  hut  their  use  is  limited,  and  the  arsenic 
is  determined  only  as  arsenious  oxide. 

3 

O.B. Winters,  of  the  Michigan  Agricultural  Station,  reports 
work  there  on  the  determination  of  lead,  copper,  zinc,  in  such 
mixtures  as  Bordeaux-lead  arsenate,  zinc  arsenite  etc.;  and  a 
comparison  of  the  Gyory-Bromate  method  with  the  officiiil  Iodine 
method,  for  determining  arsenic  when  present  in  hydrochloric 
acid  solution.  The  results  obtained  \yith  the  Gyory  method  were 
promising.  Moreover  good  results  were  also  obtained  with  the 
distillation  method  of  determining  the  total  arsenic  in  London 
Purple. 

J.J.T. Graham  tested  out  several  methods  and  made  the 
following  reports:  the  Bromate  method  for  the  determination 

of  the  total  arsenic  is  carried  out  ini  the  following  manner: 
proceed  as  directed  under  the  official  distillation  melthod, 
until  the  distillate  is  made  to  a liter  in  volume.  l.Take  ali- 
quot  parts  of  200  cubic  centimeters,  heat  to  Centigtrade, 
and  titrate  with  standard  potassium  bromate  solution,  tising 
methyl  orange  as  an  indicator.  2. Proceed  as  in  (1.)  except  the 
titration  is  made  without  heating.  The  number  of  cubic  centi- 
meters of  standard  bromate  solution  used,  times  2 equals  the 


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percent  of  total  arsenic  in  the  sample  as  expressed  in  arsen- 
ious  oxide.  The  iodate  method:  proceed  as  under  the  distil lati 
method,  except  the  distillate  is  made  to  a rolume  of  600  cubic 
centimeters.  Transfer  100  cubic  centimeter;;  parts  to  glass 
stoppered  flasks,  add  5 cubic  centimeters  of  chloroform  and  10 
cubic  centimeters  of  hydrochloric  acid.  Titrate  with  standard 
Iodate  solution  until  the  iodine  disappears  from  the  chloro- 
form when  thoroughly  shaken. 

Graham  said  that  both  methods  checked  closely,  but  that 
the  reaction  was  slower  in  the  cold  Bromate  method,  while  the 
hot  method  here  is  very  satisfactory,  ihe  Iodate  method  gives 
accurate  results,  but  the  manipulation  is  not  so  smooth  and 
easy  as  in  the  Bromate  method. 

O.B. Winters  reports  that  he  has  tried  out  the  following 
methods;  Gyory-Bromate  method:  where  one  proceeds  as  under  the 
official  Iodine  method  except  that  the  distillate  is  made  to 
500  cubic  centimeteEs  instead  of  a thousand,  a)  Transfer  a 100 
cubic  centlmeterr,  parts  to  flasks*  Heat  to  almost  boiling  and 
and  titrate  with  standard  Bromate  solution  using  methyl  orange 
as  an  Indicator,  b)  Same  as  a except  the  solution  is  n4t  heatec 

Iodate  method:  This  is  the  same  as  the  Jamieson  method.  To 
100  cubic  centimeters  of  distillate  add  6 cubic  centimejrers  of 
chloroform  and  10  aibic  centimeters  of  concentrated  hydrochlor- 
ic acid,  and  titratefwith  standard  Iodine  solution. 

Winters  says  howelrer,  that  although  the  results  obtained 
with  this  method  are  good,  thevprocedure  is  too  long  and  the 
technique  disagreeable.  The  hot  Gyory-Bromate  method  is  good 
and  very  convenient  but  a maximum  temperature  should  be  stated 


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5. 

here.  The  cold  Bromate  method  runs  too  high,  as  the  indicator 
is  not  sensitlre  enough  in  cold  solution. 

A few  other  metho(  s that  hare  been  suggested  by  chemists 
other  than  those  reporting  to  the  Association  of  Official  Agri- 
cultural Chemists  are  as  follows: 

Oxalate  Iodine  process  for  Paris  Green  Analysis  by  C.H. 

u 

Peters  and  L.F. Fielding.  Oxalic  acid  gires  a quantitative 
separation  of  eopper  from  arsenic,  the  copper  being  precipitat- 
ed as  the  oxalate;  A .25  gram  sample  is  boiled  with  less  than 

1 cubic  centimeter  of  (1:10)  sulphuric  acid  in  a total  volume 
of  50  cubic  centimeters,  and  while  the  solution  is  still  hot, 

2 grams  of  oxalic  acid  crystals  are  added  and  the  heating  con- 
tinued. Allow  the  boiled  solution  to  stand  over  night  and  then 
filter.  The  precipitate  is  dissolved  in  water  with  sulphuric 
acid,  and  titrated  with  potassium  permanganate.  The  arsenic  is 
determined  by  titration  of  the  filtrate  with  Iodine  solution 
with  an  excess  of  sodium  bicarbonate  present.  The  results 
obtained  with  this  method  agree  with  those  of  standard  methods. 

S.S. Jamieson's  method  for  the  determination  of  arsenic  in 
insecticides  has  several  arguments  in  its  favor,  and  trivalent 

ate 

arsenic  can  be^determined  tliis  way.  A solution  in  eleven  to 
twenty  percent  hydrochloric  acid  is  titrated  with  potassium 
iodate,  using  a layer  of  chloroform  as  an  indicator.  This 
method  has  its  advantages  over  the  iodometric  method  in  that 
a standard  solution  of  potassium  iodate  is  prepared  by  weighing 
and  dissolving  to  volume,  no  further  standardization  being 
necessary.  The  solution  is  fairly  stable,  and  the  results 
obtained  by  using  this  method  check  with  those  of  other  methods 


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6. 

Method  Used. 

After  yarlous  experiments  with  new  methods  the  results  of 
the  following  method  were  found  to  check  closely  with  those  of 
others.  A .5  gram  sample  of  Paris  Green  is  dissolved  in  10  cubic 
centimeters  of  concentrated  ammonium  hydroxide,  and  the  solutioi 
made  up  to  .6  normal;  then  hydrogen  sulphide  is  passed  into  the 
evacuated  flask  containing  the  solution,  thus  precipitating  the 
copper  as  the  sulphide,  while  the  arsenic  will  remain  in  the 
filtrate  as  ammonium  sulfo-salts.  A complete  precipitation 
must  he  made.  The  solution  should  then  he  filtered  quickly  under 
vacuum,  as  the  sulphide  of  copper  is  quickly  oxidized  hack  in 
the  presence  of  air.  The  filter  paper  containing  the  copper  pre- 
cipitate is  digested  with  corct^nlrc-.tec!,  nitric  acid,  and  the  sol- 
ution heated  to  drive  off  nitrous  firaes  after  which  hraniine 
water  is  added  to  insure  complete  oxidation  of  remaining  nitrous 
acid,  after  which  the  copper  is  determined  hy  means  of  the 
usual  volumetric  method  with  tenth  normal  sodium  thiosulphate. 

.he  filtrate  containing  the  ctrsenic  is  heated  to  d±ive  off 
the  excess  hydrogen  sulphide,  after  vdiicli  the  solution  is  neu- 
tiralized  with  concentrated  hydrochloric  acid,  and  then  made  up 
to  a (1:1)  acid  concentration  with  hydrochloric  acid,  placed  on 
the  steam  b«th,  and  oxidized  with  potassium  chlorate  toa  bead  of 
sulphur  xo  this  oxidized  solution  potassium  iodide  is  added, 
and  the  solution  titrated  with  tenth  normal  sodium  thiosulphate, 
after  which  it  is  neutralized  with  sodium  hicarhonate,  an  excess 
of  10  grams  added,  and  then  titrated  with  tenth  normal  iodine 
solution® 


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7 


Part  ri. 

xhe  Ratio  of  Potassiurii  Iodide  to  Copper  in  the  lodoraetric  Metho^  . 

In  connection  with  the  work  on  the  io dome trie  method  of  de- 
termining copper  this  prohljia  suggested  itself,  as  to  whether 
or  not  the  same  amount  of  iodine  was  liberated  when  cuprous 
iodide  was  precipitated  on  the  addition  of  potassium  iodide,  or 
when  the  precipitate  formed  dissolred  when  an  excess  of  potass- 
ium iodide  was  used. 

^^ith  regard  to  this  subject  Peters  says  in  his  paper,  that 
it  has  been  suggested  by  Bray  and  Mciiaj?  that  failure  of  stand- 
ardizations to  check  , may  be  due  to  adsorption  or  solution  of 
some  of  the  iodine  by  the  precipitated  cuprous  iodide,  with  the 
result  that  a too  low  titration  value  of  the  sulphate  is  given 
aagner  agrees  that  the  standardization  of  tnio sulphate  by 
iodates  in  acid  solutions  is  accurate  He  found  that  the  con- 
centration of  potassium  iodide  made  no  difference  and  the  theor  '■ 
of  adsorption  did  not  hold  good,  but  the  concentration  of 
potassium  iodide  should  be  high  it  comparison  to  the  equivalent 
of  copper  present.  The  most  important  point  is  that  the  concen- 
tration of  iodide  be  high  in  relation  to  the  final  volume  at 
the  completion  of  the  titration-  This  point  was  developed  by 
Gooch  and  Heath.  Tliey  claimed  that  the  accuracy  of  results  ob- 
tained oy  the  iodide  method  is  affected  by  (a)  varying  concen- 
trations of  mineral  acids, (b)  by  the  presence  of  salts  both 
independently  of  anci  in  conjunction  with  acetic  and  mineral 
acids. 

ticClure  states  that  cuprous  iodide  will  be  precipitated  and 

iodine  exactly  proportional  to  the  ammount  of  copper  present 
will  be  liberated,  and  be  held  in  solution  in  the  excess  of 


8 


potassium  iodide. 

In  the  present  experiment  a standard  solution  of  chemically 
pure  copper  sulphate  solution  was  made#  and  aliquot  portions  of 
10  cubic  centimeters  were  used*  These  were  made  acid  with  5 cubi 
centimeters  of  acetic  acid  and  varying  amounts  of  potassium 
iodide  added  and  the  solutions  titrated  with  sodium  thiosulphate 
which  was  tenth  normal. 


n. 


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r ‘ ’■  "W  " 

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.■i'W"%-f  .^ . '!, ‘'3' 


9 


,^xperi)Tiental  • 

A decision  was  made  after  various  experiments  to  use  as  a 
unit  a sample  of  approxiraately  •5/of  a gram  of  Paris  Green* 

This  Wos  dissolved  in  concentrated  ammonium  hydroxide  dnd  the 
copper  precipitated  as  the  sulphide  with  hydrogen  sulphide.  The 
solution  was  found  to  be  very  difficult  to  filter, hut  at  length 
was  accomplished  hy  filtering  under  suction  and  keeping  the 
funnel  well  filled  and  covered.  The  copper  sulphide  then  was 
taken  into  solution  with  nitric  acid  and  the  copper  determined 
in  the  usual  manner  with  sodium  thiosulphate.  The  results  of 
the  work  on  the  copper  were  as  follows: 


Sample  weight 

Thiosulphate  used 

Ber  cent  vopper 

.5326 

20.25  c*c. 

24.29  fo 

.5035 

19.05  c.c. 

24.17  fo 

.5902 

22.60  c.c. 

24.47  f 

.5090 

19.20  c.c. 

24.10  f 

.5501 

20.40  c.c. 

23.69  f 

.5725 

21. 10  c.c* 

23.53  f 

.5011 

18.40  c.c. 

23.46  f 

.5171 

18.50  6.C. 

22.86  f 

.5000 

18 . 45  C.c* 

23.57  °/c 

Factor  of  thiosulphate  = grams  of  copper  per  c.c. 


10 


Several  methods  were  employed  in  the  work  with  the  arsenic 
"vi/hen  the  filtrate,  light  yellow  in  color,  containing  the  arsen 
ic  was  hoiled,  instead  of  becoming  colorless,  it  turned  a rich 
golden  broim  which  faded  on  cooling  to  the  original  color, 
attempt  was  made  to  oxidize  the  sulphur  in  the  alkaline  solu- 
tion with  hydrogen  peroxide  or  sodium  peroxide  to  a sulphate, 
and  at  the  same  time  converting  the  arsenic  entirely  to  the 
arsenate.  Sodium  peroxide  was  found  to  be  the  better  oxidizing 
agent  in  this  case  and  a 30  gram  portion  was  found  necessary 
so  that  upon  heating  the  solution  became  colorless.  However, 
upon  making  the  solution  acid  with  hydrochloric  acid  a precip- 
itate started  to  appear  and  soon  ferric  hydroxide  came  domi 
followed  by  arsenic  in  various  stages  until  it  was  at  length 
all  precipitated  as  the  sulphide. 

To  correst  this  the  solutian  was  made  alkaline  with  sodium 
hydroxide,  and  the  amount  of  sodium  peroxide  then  needed  to  be 
added  in  excess,  after  the  solution  had  become  colorless,  in 
ordefi  to  take  care  of  all  the  arsenic  as  well  as  the  sulphur 
was  found  to  be  20  grams,  ^fter  strongly  acidifying  with  hydro- 
chloric acid  potassium  iodide  vras  addea  and  the  solutmn  tit- 
rated  w$th  tenth  normal" iodine  solution,  however  the  results 
of  this  method  did  not  prove  constant,  and  the  mechanical  work 
was  not  smooth.  So  at  length  the  filtrate  was  made  (l:i)  acid 
with  hydrochloric  acid  to  begin  with  and  oxidized  with  potass- 
ium chlorate,  and  the  titration  then  carried  out  in  a similar 
manner.  This  proved  quite  satisfactory. 

^-^■sodiuni  thiosulphate  solution,  made  neutral  and  an  excess  of 
sodium  bicarbonate  added  when  the  reduced  arsenic  was  titrated 
v/ith  tenth  normal 


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11 


Results  of  Arsenic  jD^ terminations. 


Sample  weight. 

Xodine 

used 

Arsenio 

.5000 

58.10 

c .c. 

57.51 

.5000 

66.50 

c.c* 

65.83 

.5000 

63.10 

6 . c . 

62.40 

.5000 

57.05 

c.c. 

57.37 

.5000 

57.25 

c.c. 

56.68 

.5000 

57.40 

© . c . 

56.82 

rif 

T 

.5000 

57.t)5 

c .c» 

57.07 

lc.c«  iodine  solution  = .00495  grams  arsenious  oxide. 


Results  of  Experimental  work  on  the  Ratio  of  Potassium 
iodide  to  Copper  in  the  lodometric  Method. 


S-ample 

Acid  used 

Kl  used 

Thiosulphate 

Salt  fonnec 

10  © • c . 

5 c.c. 

0.7513  ^rans 

13 .OOc.c. 

s&ngl e 

10 

5 

n.7504 

13.90 

10 

5 

0.7511 

13.85 

10 

o 

1.0040 

13.85 

single 

10 

5 

1.0045 

13.85 

10 

5 

1.0004  " 

13.85 

10 

U 

1.2520  “ 

13.85 

single 

10 

5 

1.2535 

13.80 

10 

5 

1.2503 

13.85 

10 

5 

1.5270 

13.85 

single 

10 

5 

1.5020 

13.85 

10 

5 

1.520 

13.90 

12 


Sample 

@cid  used 

|(l  used 

Thiosulphate 

^al  t 

10c. c. 

5c.«. 

1.7520 

graans 

13.85c  »c « 

single 

10 

5 

1.7539 

II 

13.85 

10 

5 

1.7532 

f! 

13.85 

10 

5 

2.0012 

II 

13.80 

single 

10 

5 

2.0003 

ft 

13.85 

10 

5 

2.0011 

li 

13.85 

10 

5 

2.5014 

li 

13.85 

single 

10 

2.5012 

M 

13.85 

10 

5 

2.5000 

13.85 

10 

5 

2.7509 

13.85 

bigg±e 

10 

5 

2.7520 

-• 

13.85 

10 

5 

2.7531 

n 

13.85 

10 

5 

3.0018 

ft 

13.85 

single 

Id 

5 

3.2514 

Tt 

13.85 

10 

5 

3.2616 

•• 

13.85 

10 

5 

3.5021 

•t 

13.85 

o ingle 

10 

5 

3.5016 

13.85 

10 

5 

3.5024 

13.85 

10 

5 

3.7504 

13.35 

siiigle 

10 

5 

3.7516 

13.35 

10 

5 

4.0020 

13.35 

single 

10 

5 

4.001f? 

13.85 

10 

5 

4.0024 

tf 

13.85 

Sample 

Acid  used 

13. 

used 

Thiosulphate  ^iilt 

10  c . c . 

5 c*c • 

4. 500 2 

,'^raias 

13.85 

$ingle 

10 

5 

4.5014 

n 

13.85 

10 

5 

4.5021 

-• 

13.85 

10 

5 

5.0008 

13.90 

singl e 

10 

5 

5.0014 

13.85 

10 

5 

5.0021 

tl 

13.85 

10 

5 

5.5018 

fl 

13.85 

singl e 

10 

5 

5 . 5024 

tl 

13.85 

10 

5 

5.5002 

n 

13.85 

10 

5 

G.0026 

If 

13.85 

_ ingl e 

10 

5 

6.0014 

n 

13.85 

10 

5 

6.0006 

13.85 

10 

5 

O.5010 

13.85 

single 

10 

5 

6.5021 

•• 

13.85 

10 

5 

6.7521 

n 

13.85 

single 

10 

5 

6.7504 

ti 

13.85 

10 

5 

657516 

I! 

13.85 

10 

5 

7.0007 

13.90 

^ouhiS 

10 

5 

7.0016 

•• 

13.85 

10 

5 

7.0021 

n 

13.85 

10 

5 

7.5002 

II 

13.85 

aouhle 

10 

5 

7.5004 

13.90 

10 

5 

7.5021 

ir 

13.85 

10 

5 

8.0004 

II 

13.85 

double 

10 

5 

8.5016 

13.35 

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14 


onclusion. 

Of  the  methods  employed,  the  results  with  copper  proved 
satisfactory,  and  the  last  one,  that  of  oxidizing  the  arsenic 
solution  with  potassium  chlorate,  gave  good  results  also* 

So  we  present  as  a nexT  metuod  for  the  analysis  of  Pasis 
Green  the  precipitation  of  the  copper  as  the  sulphide  followed 
hy  an  iodometric  titration  for  the  determination  of  the  copper 
content,  and  that  of  oxidizing  the  arsenic  in  hydrochloric 
acid  solution  folloxFed  hy  the  titrations  with  thiosulphate 
and  iodine  for  the  determination  of  the  arsenic  content* 

Moreover  the  same  amount  of  Todine  is  liberated,  whether  o: 
not  a precipitate  is  given  upon  the  addition  of  potassium 
iodide  to  copper  sulphate  solution  when  titrated  X7ith  sodium 
thiosulphate# 


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Bibliography. 


1.  Roark  R.C.  J.  Ass.  Of  . A§r.  Chemists.  Vol  1.  1915rl9l6. 

2.  Roark  R.C.  J.  Ass.  Of  . Agr.  Chemists.  Vol  3*  Page  157» 

3.  Winter  O.B.  J.  ®ss.  Of.  Agr.  Chemists.  Vol  4.  Page  134-^7,  191 

4.  Graham  J.J.T.  J.  Ass.  Of. Agr.  Chemists.  Vol  5*  iTo1  .Page  33,  *2 

5.  Winter  O.B.  J.Ass.  Of.  Agr.  Chemists.  Vol  4.  No3.Page  395, '2 

6.  Peters  C.A.&  Fielding  L.F.  J.  Ind.  Fng.  Chem. 

Vol. 8 Page  1114-5  1916. 

7.  Jamieson  S.S.  J. Ind. Eng.  Chem.  Vol  10.  Page  290-2  1018. 

8*„Deters  J.Am.  Chem.  Soc.  Vol  34.  Page  422. 

9.  McClure  L.D.  Min.&Sci,  Press.  Vol  103*Page  48. 

10.  Graham  J.J.T.  J.Ass.  Of.  Agr.  Chemists.  Vol5  No. 3 Page  392-40 


0 


